Vibration driven motor

ABSTRACT

In a vibration driven motor, a rotatable member is brought into frictional contact with a vibration member having an electro-mechanical energy conversion element and by the application of an AC electric field to the electro-mechanical energy conversion element, a driving vibration is excited in the vibration member to drive the rotatable member. A rotation output member is provided for frictionally contacting the rotatable member to deliver an output, and the frictional force between the rotatable member and the rotation output member is set to a value smaller than the frictional force between the vibration member and the rotatable member.

This application is a division of application Ser. No. 08/034,182 filedMar. 18, 1993, now U.S. Pat. No. 5,428,260, which is a continuation ofapplication Ser. No. 07/739,493 filed Aug. 2, 1991 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an ultrasonic motor (hereinafter also referredto as a vibration driven motor) endowed with the friction clutchfunction.

2. Related Background Art

In recent years, a vibration driven motor or a so-called bar-likevibration driven motor in which electrical signals differing in phasefrom each other are applied, for example, to piezoelectric elements aselectro-mechanical energy conversion elements to thereby generate aplurality of bending vibrations differing in phase in time in differentplanes of a vibration member, whereby circular or elliptical motion isexcited in the surface of the vibration member of a metal or the like tocause relative movement between a member (e.g. a rotor) in contact withsaid surface and said vibration member has been proposed, for example,in U.S. Pat. No. 4,562,374.

In this bar-like vibration driven motor, the vibration member and therotor cannot be disposed so as to surround, for example, thephoto-taking lens of a camera as in a well-known ring-like vibrationdriven motor. Therefore, it is unavoidable to adopt a construction inwhich the rotational force of the rotor is transmitted to a drivenmember, for example, a focusing lens through a transmission mechanismsuch as a gear.

However, where the driven member (for example, the lens) is driventhrough the transmission mechanism such as a gear with the bar-likeultrasonic motor as a drive source, if a high load is applied to arotation output member such as a gear for transmitting the rotationalforce of the rotor to the driven member, the rotation of the rotorbecomes unstable. In the worst case, the vibration member of the motordeviates from its resonant state and the rotation of the rotor stops.This has led to the problem that, although the vibration member is beingexcited, the rotor stops at that location, thereby causing the creationof sounds (noises) or the creation of abnormal abrasion between thestator (vibration member) and the rotor.

So, in order to solve such a problem, in Japanese Laid-Open PatentApplication No. 2-97281, design is made such that if a high load isapplied, the rotor is idly rotated. However in this system, it isnecessary to newly provide a friction plate between the rotor and theoutput shaft, and this could not be said to be effective in respect ofspace and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve such a problempeculiar to the prior art and to provide an ultrasonic motor in whichthe creation of abnormal abrasion and abnormal sound between a rotor anda stator can be prevented even if a high load is applied from theoutside to a driving system.

It is another object of the present invention to provide, in addition tothe above object, an ultrasonic motor which can be made compact.

Other objects of the present invention will become apparent from thefollowing detailed description of the invention.

One aspect of the present invention is that a rotatable member isbrought into frictional contact with a vibration member having anelectro-mechanical energy conversion element and by the application ofan AC electric field to the electro-mechanical energy conversionelement. A driving vibration is excited in the vibration member to drivethe rotatable member. A rotation output member is provided forfrictionally contacting the rotatable member to deliver an output, andthe frictional force between the rotatable member and the rotationoutput member is set to a value smaller than the frictional forcebetween the vibration member and the rotatable member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and lB are a plan view and a cross-sectional view,respectively, showing an embodiment of a vibration driven motoraccording to the present invention.

FIG. 2 is a cross-sectional view of an embodiment in which the motor ofthe present invention is applied for the driving of the lens barrel of acamera.

FIG. 3 is a cross-sectional view of a transmission mechanism in theembodiment of FIG. 2.

FIG. 4 is a cross-sectional view of another embodiment of the presentinvention.

FIG. 5 is a cross-sectional view of an apparatus for driving the lensbarrel shown in FIG. 4.

FIG. 6A is a plan view of another embodiment of the present invention.

FIG. 6B is a cross-sectional view of the motor shown in FIG. 6A.

FIGS. 7A and 7B are a plan view and a cross-sectional view,respectively, of another embodiment of the present invention.

FIGS. 8A and 8B are a plan view and a cross-sectional view,respectively, of another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinafter be described in detail withrespect to some embodiments thereof shown in the drawings.

FIG. 1 shows an embodiment of a vibration driven motor according to thepresent invention, FIG. 1A being a plan view thereof, and FIG. 1B beinga vertical cross-sectional view thereof.

The reference numeral 1 designates a pillar-shaped vibratory resilientmember formed of a metallic material, the reference numeral 2 denotes akeep member formed of a metallic material and having an outer diametersimilar in shape to the outer diameter of the vibratory resilient member1, the reference characters 3a-3d designate circular ring-shapedpiezoelectric elements as electro-mechanical energy conversion elementsformed with an outer diameter equal to the outer diameter of thevibratory resilient member 1, and the reference characters 4a-4d denotethe electrode plates of the piezoelectric elements 3a-3d. The electrodeplates 4a-4d and the piezoelectric elements 3a-3d are disposed betweenthe vibratory resilient member 1 and the keep member 2, and a bolt 5 isthreadably engaged with the vibratory resilient member 1 through thekeep member 2, whereby these are. fixed as a unit and constitute thestator of the vibration driven motor A.

The vibration driven motor A is such that AC voltages differing inelectrical phase are applied from a power source circuit, not shown, tothe electrode plates 4a-4d of the stator, whereby the piezoelectricelements 3a-3d form two-direction bending vibrations in the differentplanes of the stator and differing in phase in time in the stator, and amotion like rope skipping is excited in the stator by a combination ofthese bending vibrations, whereby a rotor 6 to be described which is infrictional contact with the fore end portion of the stator isfrictionally driven. The rotor 6 has its rear end portion (frictionalcontact portion) 6a bearing the tapered portion 1a of the vibratoryresilient member 1, and obtains an appropriate frictional force by thepressing provided by a pressing spring 10 which will be described later.

The reference numeral 7 designates a rotation output member of afriction stabilizing material having a gear 7a is friction-coupledbetween the rear end surface thereof and the end surface of the rotor 6.The gear 7a is for transmitting the rotation of the rotor 6 to theoutside, for example, the photo-taking lens driving mechanism 7b of acamera.

The frictional force of the friction coupling between the rotor 6 andthe rotation output member 7 is created by the pressing spring 10, andthat force is set so as to be smaller than the frictional force betweenthe vibratory resilient member 1 and the rotor 6 (that is, thecoefficient of friction between the rotor 6 and the member 7 may besmaller than that between the resilient member 1 and the rotor 6).

That is, even if a rotational force is given from the outside to therotation output member 7, the rotor 6 will not rotate but only therotation output member 7 will rotate because the forcibly frictionalforce to the stator is greater than the frictional force to the rotationoutput member 7.

On the other hand, a bearing 8 is provided in the bore portion of therotation output member 7, and a hollow shaft 9 is fitted into the boreportion of the bearing 8 to thereby make the rotor 6 and the rotationoutput member 7 rotatable.

The shaft 9 is fitted in the sliding portion 5a of the bolt 5 to therebymake the sliding portion coincident with the axis of the stator.

The pressing spring 10 is designed to press the stepped portion 9a ofthe shaft 9 to thereby press the bearing 8 by the flange portion 9b ofthe shaft 9 and create a frictional force between the vibratoryresilient member 1 and the rotor 6 and between the rotor 6 and therotation output member 7 by that pressing force.

The pressing force of the pressing spring 10 is produced by a well-knownmethod of inserting the hole portion of a planar holding member 11 ontoa pin portion 5b formed on the tip end portion of the bolt 5, andadhesively securing, for example, the hole portion 11c to the pinportion 5b.

This vibration driven motor A is fixed by fixing the holding member 11to a fixed member, not shown, by screws, not shown, through screw holes11a and 11b.

When supporting the stator of the vibration driven motor, it isnecessary to prevent the vibration excited by the stator from beingaffected. The end of the stator is the antinode position of thevibration and at that end, there is only displacement in the diametricaldirection and moreover this displacement is actually minute andtherefore, by fixing the pin portion 5b which is one end of the stator,the vibration of the stator is prevented from being affected.

In the thus constructed vibration driven motor, when a high load isapplied to the rotation output member 7, the rotor 6 begins to sliderelative to the rotation output member 7 before the rotation of therotor 6 becomes unstable or stops, and the high load from the rotationoutput member 7 is not transmitted between the rotor 6 and the stator.

To establish the operation as described above, the choice of thematerials of the vibratory resilient member 1, the rotor 6 and therotation output member 7 becomes a subject, and when a combination ofbrass for the vibratory resilient member 1 and aluminum for the rotor 6was used and the coefficient of friction therebetween was 0.8 or moreand polyacetal was used for the rotation output member 7 and thecoefficient of friction between the rotor 6 and the member 7 was 0.2 orless and the above-described operation was performed, it was confirmedthat the motor operates well. It was also confirmed-that these materialsare not restrictive and if there is a difference in coefficient offriction about four times as great, the rotor 6 and the rotation outputmember 7 slide positively before the vibratory resilient member 1 andthe rotor 6 slide.

As shown, the vibratory resilient member 1, the rotor 6 and the rotationoutput member 7 are formed with substantially the same diameter, and theholding member 11 is constructed so as to be substantially equal to orlarger in diameter than the vibratory resilient member 1, the rotor 6and the rotation output member 7, and these are integrally assembledinto a unit.

FIG. 2 is a cross-sectional view showing an embodiment in which themotor according to the present invention is applied to the lens barrelof a camera, and FIG. 3 shows the transmission mechanism thereof.

The reference numerals 15, 16 and 17 designate gears for transmittingthe rotation of the rotation output member 7. These gears are arrangedas shown, and the gear 15 has one end portion of its rotary shaftsupported on a motor ground plate 12 and has the other end portionsupported by a screw 14 threadably engaged with the hole portion of theholding member 11. The gear 17 is fixed to the rotary shaft of the gear16 to transmit the output of the vibration driven motor to the rotatablecylinder 18 of the lens barrel. The reference numeral 21 denotes a gearto which a pulse plate 20 is secured and which meshes with the gear 16.The pulse of the pulse plate 20 may be read by a photocoupler 22,whereby for example, the movement, the position, etc. so the rotatablecylinder 18 which is a driven member rotatively driven by the gear 17can be detected.

In this lens barrel, the helicoid thread portion 18a of the rotatablecylinder 18 having a lens L for effecting focusing or zooming ishelicoid-coupled to a helicoid thread portion 19a provided on a fixedcylinder 19. By this rotatable cylinder 18 being moved along thedirection of the optical axis while being rotated, the focusing orzooming operation is performed, and for the driving of the motor, thegear 17 is in meshing engagement with a gear portion 18b provided on therotatable cylinder 18. The motor ground plate 12 is fixed to the fixedcylinder 19.

As regards the operation of an apparatus for driving the thusconstructed lens barrel, in response to a lens driving signal from adriving circuit, not shown, which is provided, for example, in a camera,not shown, AC voltages are applied to the electrode plates 4a-4d of themotor A, whereby as previously described, the rotor 6 is rotated in apredetermined direction (the direction of rotation is determined byreversing, for example, the advance of the phases of the applied two ACvoltages differing in phase from each other). By the rotation of therotor 6, the rotation output member 7 which is frictionally coupled tothe rotor 6 is also rotated, and the rotation output thereof istransmitted through the gear 15, the gear 16 and the gear 17 to rotatethe rotatable cylinder 18. The rotatable cylinder moves forward orbackward while being rotated to thereby accomplish focusing or zooming,and at the same time, the lens position or lens movement information isoutput from the photocoupler 22.

On the other hand, if a rotational force is imparted from the outside tothe rotatable cylinder 18 when the vibration driven motor isinoperative, the gear 17 is rotated and thus, the gear 16 and the gear15 are also rotated, and the rotation output member 7 is also rotated.

However, since as previously described, the frictional force between therotation output member 7 and the rotor 6 is set to a value smaller thanthe frictional force between the stator and the rotor 6, the rotor 6 isnot rotated and the rotation output member 7 slides and rotates withrespect to the rotor 7.

FIG. 4 shows another embodiment of the present invention in which aholding member is used also as the thrust receiver of a memberconstituting a transmission mechanism.

A vibration driven motor A similar in construction to the aforedescribedvibration driven motor is fixed by a holding member 11A being secured toa motor ground plate 12 which is a fixed member by screws 13 and 14,while this holding member 11A serves also as the thrust receiver of thegears 15 and 21 of a transmission mechanism which will be describedlater.

FIG. 5 is a cross-sectional view of an apparatus for driving a lensbarrel by the use of the vibration driven motor shown in FIG. 4.

In this lens barrel, the helicoid thread portion 18a of a rotatablecylinder 18 having a lens L for effecting focusing or zooming ishelicoid-coupled to a helicoid thread portion 19a provided on a fixedcylinder 19. By this rotatable cylinder 18 moving along the direction ofthe optical axis while being rotated, the focusing or zooming operationis performed, and the gear 17 of the motor driving apparatus is inmeshing engagement with a gear portion 18b provided on the rotatablecylinder 18. The motor ground plate 12 is fixed to the fixed cylinder19. Thus, the photo-coupler 22 detects the movement and position of thelens.

FIG. 6 shows an embodiment of the vibration driven motor according tothe present invention, FIG. 6A being a plan view thereof, and FIG. 6Bbeing a vertical cross-sectional view thereof. Elements functionallysimilar to those shown in the above-described embodiments are givensimilar reference characters and need not be described.

In the present embodiment, as shown, the vibratory resilient member 1,the rotor 6 and the rotation output member 7 are formed withsubstantially the same diameter, and the holding member 11 is formed soas to be substantially equal to or larger in diameter than the vibratoryresilient member 1, the rotor 6 and the rotation output member 7, andthe holding member 11 functions as a guard member when the motor body isto be kept in a case, not shown, or is to be assembled to an apparatus.

Although the vibratory resilient member 1, the rotor 6 and the rotationoutput member 7 are formed with substantially the same diameter, thesemay differ in diameter from one another, and in such case, the diameterof the holding member may be made equal to or larger than the greatestone of the diameters of these parts.

FIG. 7 shows an embodiment of the vibration driven motor according tothe present invention, FIG. 7A being a plan view thereof, and FIG. 7Bbeing a vertical cross-sectional view thereof.

The reference numeral 1 designates a pillar-shaped vibratory resilientmember, the reference numeral 2 denotes a keep member formed of ametallic material and having an outer diameter equal to the outerdiameter of the vibratory resilient member 1, the reference characters3a-3e designate circular ring-shaped piezoelectric element plates formedwith an outer diameter equal to the outer diameter of the vibratoryresilient member 1, and the reference characters 4a-4e denote theelectrode plates of the piezoelectric element plates 3a-3e. Theelectrode plates 4a-4e and the piezoelectric element plates 3a-3e arealternately disposed as shown between the vibratory resilient member 1and the keep member 2, and a bolt 5 is threadably engaged with thevibratory resilient member 1 through the keep member 2, whereby theseare integrally fixed to constitute the stator of the vibration drivenmotor A.

The vibration driven motor A is such that AC voltages differing in phasefrom one another are applied from a power source circuit, not shown, tothe electrode plates 4a-4e of the stator, whereby the piezoelectricelement plates 3a-3e form mechanical vibrations in the stator, and by acombination of these vibrations, a motion like rope skipping is excitedin the stator to frictionally drive a rotor 6 to be described which isin frictional contact with the fore end portion of the stator.

The rotor 6 has its rear end portion (frictional contact portion) 6abearing against the tapered portion 1a of the vibratory resilient member1, and obtains an appropriate frictional force by the pressing by apressing spring 10 which will be described later. The reference numeral7 denotes a rotation output member formed of a friction stabilizingmaterial and having a gear 7a, and is friction-coupled between the rearend surface thereof and the end surface of the rotor 6. The gear 7a isfor transmitting the rotation of the rotor 6 to the outside.

The frictional force of the friction coupling between the rotor 6 andthe rotation output member 7 is created by the pressing spring 10, andthat force is set so as to be smaller than the frictional force betweenthe vibratory resilient member 1 and the rotor 6 (so that thecoefficient of friction may be small). That is, even if a rotationalforce is given from the outside to the rotation output member 7, therotor 6 will not rotate. Rather only the rotation output member 7 willrotate because the frictional force to the stator is greater than thefrictional force to the rotation output member 7.

On the other hand, a rotation output bearing member 8 of a low frictionmaterial such as resin integrally movable relative to the rotationoutput member 7 in the direction of rotation and having a degree offreedom in the thrust direction is provided in the bore portion of therotation output member 7, and this rotation output bearing member 8 isrotatably fitted on a shaft 9. Shaft 9 is forced into the bolt 5 andmade integral with the bolt 5. The pressing spring 10 is designed topress the flange portion 7b of the rotation output member 7 and create africtional force between the vibratory resilient member 1 and the rotor6 and between the rotor 6 and the rotation output member 7 by thepressing force of the pressing spring. The pressing spring 10 pressesthe rotation output bearing member 8 to bring this rotation outputbearing member 8 into pressure contact with a planar holding member 11,thereby holding the pressing force of the pressing spring 10.

The frictional force of the portion of pressure contact between therotation output bearing member 8 and the holding member 11 is set to avalue smaller than the frictional force between the rotation-outputmember 7 and the rotor 6. That is, the relation among the frictionalforce F₁ between the rotation output bearing member 8 and the holdingmember 11, the frictional force F₂ between the rotation output member 7and the rotor 6, and the frictional force F₃ between the rotor 6 and thevibratory resilient member 1 is set so that F₁ <F₂ <F₃. The holdingmember 11 is set against slippage relative to the shaft 9 by a push nut12, and is stopped from rotating relative to the shaft 9 by a detentmechanism against the shaft 9. This vibration driven motor A is fixed byfixing the holding member 11 to a fixed member, not shown, by screws,not shown, through screw holes 11a and 11b.

The operation of the vibration driven motor A will now be described.

When AC voltages are applied to the electrode plates 4a-4e, thepiezoelectric element plates 3a-3e are vibrated and thus, the rotor 6 isrotated in a predetermined direction through the vibratory resilientmember 1. The direction of this rotation is determined by reversing, forexample, the advance of the phases of the applied two AC voltagesdiffering in phase from each other.

The rotation of the rotor 6 causes the rotation of the rotation outputmember 7 frictionally coupled to the rotor 6. At that time, the rotationoutput bearing member 8 is also rotated with the rotation output member7, but as previously described, by the balance between the frictionalforces, it slides and rotates between the holding member 11 and therotation output bearing member 8 and therefore, no slippage takes placebetween the rotation output member 7 and the rotor 6 and the rotationalforce of the rotor 6 can be transmitted to the outside by the gearportion 7a of the rotation output member 7. With the rotation of therotation output member 7, the pressing spring 10 is also rotated, butthe pressing spring 10 is of such structure that is only presses in thethrust direction and transmits the rotation without the intermediary ofthe pressing spring 10 and therefore, the rotation of the rotationoutput member 7 is effected smoothly without being subjected to thetorsion, distortion, flexure, chatter, etc. of the pressing spring 10for the rotation of the rotation output member 7.

Also, when a high load is applied to the rotation output member 7, therotor 6 begins to slide relative to the rotation output member 7 beforethe rotation of the rotor 6 becomes unstable or stops, and thus, thehigh load from the rotation output member 7 is not transmitted betweenthe rotor 6 and the stator.

FIG. 8 shows another embodiment. In FIG. 8, members similar to thoseshown in FIG. 7 are given similar reference characters and need not bedescribed.

The reference numeral 101 designates a rotor having its rear end portion(frictional contact portion) bearing against the tapered portion 1a ofthe vibratory resilient member 1 to obtain an appropriate friction forcewith respect to the vibratory resilient member 1 by the pressing-by thepressing spring 10. The reference numeral 102 denotes a rotation outputmember made of a friction stabilizing material and having a gear 102a,and is friction-coupled between the rear end portion thereof and the endsurface of the rotor 101. The gear 102a is for transmitting the rotationof the rotor 101 to the outside.

The frictional force of the friction coupling between the rotor 101 andthe rotation output member 102 is created by the pressing spring 10, andthat force is set so as to be smaller than the frictional force betweenthe vibratory resilient member 1 and the rotor 101 (so that thecoefficient of friction may be small). That is, even if a rotationalforce is given from the outside to the rotation output member 102, therotor 101 will not rotate. Rather only the rotation output member 102will rotate because the frictional force to the stator (the vibratoryresilient member 1) is greater than the frictional force to the rotationoutput member 102.

On the other hand, a rotation output bearing member 103 of a lowfriction material such as resin is provided in the bore portion of therotation output member 102, and this rotation output bearing member 103is friction-coupled between the end surface of the flange portion 103athereof and the end surface of the rotation output member 102. Thefrictional force of the friction coupling between the rotation outputmember 102 and the rotation output bearing member 103 is created by thepressing force 10, and that force is set so as to be smaller than thefrictional force between the rotor 101 and the rotation output member102.

That is, the relation among the frictional force F₁ between the rotationoutput bearing member 103 and the rotation output member 102, thefrictional force F₂ between the rotation output member 102 and the rotor101, and the frictional force F₃ between the rotor 101 and the vibratoryresilient member 1 is set so that F₁ <F₂ <F₃. The rotation outputbearing member 103 is provided with pin portions 103b and 103c, whichare fitted in apertures 104a and 104b in the holding member 104, wherebythe rotation output bearing member 103 is disposed so as to be lockedwith respect to the direction of rotation and to have a degree offreedom with respect to the thrust direction. Thus, the frictionalforces F₁, F₂ and F₃ are created by the pressing spring 10. The holdingmember 104 is set against slippage relative to the shaft 9 by the pushnut 12, and is stopped from rotating relative to the shaft 9 by thedetent mechanism against the shaft 9. This vibration driven motor B isfixed by fixing the holding member 104 to a fixed member, not shown, byscrews, not shown, through screw holes 104c and 104d. Also, as in FIG.7, the output of the vibration driven motor B is transmitted to theoutside by the gear portion 102a of the rotation output member 102.

The operation of the vibration driven motor B will now be described.

When AC voltages are applied to the electrode plates 4a-4e, thepiezoelectric element plates 3a-3e are vibrated and thus, the rotor 101is rotated in a predetermined direction through the vibratory resilientmember 1 (the direction of this rotation is determined by reversing, forexample, the advance of the phases of the applied two AC voltagesdiffering in phase from each other). The rotation of the rotor 101causes the rotation of the rotation output member 102 friction-coupledto the rotor 101. At that time, as previously described, by the balancebetween the frictional forces, it slides and rotates between therotation output bearing member 103 and the rotation output member 102and therefore, no slippage takes place between the rotation outputmember 102 and the rotor 101 and the rotational force of the rotor 101can be transmitted to the outside by the gear portion 102a of therotation output member 102. The pressing spring 10 is of such structurethat is only presses in the thrust direction and transmits the rotationwithout the intermediary of the pressing spring 10 and therefore, therotation of the rotation output member 102 is effected smoothly withoutbeing subjected to the torsion, distortion, flexure, chatter, etc. ofthe pressing spring 10 for the rotation of the rotation output member102.

As in the embodiment shown in FIG. 7, when a high load is applied to therotation output member 102, the rotor 101 begins to slide relative tothe rotation output member 102 before the rotation of the rotor 101becomes unstable or stops, and thus, the high load from the rotationoutput member 102 is not transmitted between the rotor 101 and thestator.

As described above, according to the present invention, even if a highload is applied to a rotation output member such as a gear, a rotatablemember such as a rotor begins to slide relative to the rotation outputmember before the rotation of the rotatable member becomes unstable orstops, whereby the creation of abnormal abrasion and abnormal soundbetween the vibration member and the rotatable member can be prevented.

Also, according to the above-described embodiments, the frictionaldriving to the rotatable member is effected by the rotation outputmember itself and therefore, it is unnecessary to newly provide a partand thus, there can be provided a vibration driven motor which isinexpensive and is not increased in space but can contribute tocompactness.

Also, if members constituting the motor including the friction mechanismare assembled as a unit, it will become unnecessary to provide amechanism as a countermeasure for high load in any other portion thanthe motor, for example, a transmission system for driving the drivenportion, as in the prior art, and the degree of freedom of theapplication to various apparatuses will greatly increase, and the effectthereof is great.

I claim:
 1. An apparatus including a movable element, said apparatuscomprising:a vibration member for generating a vibration therein inresponse to an applied electrical signal, said vibration member having afixed axis; an annular rotor arranged for rotation about the fixed axisof said vibration member, in sliding frictional contact with saidvibration member to drive said annular rotor about the fixed axis byvibration generated in said vibration member; a moving mechanism formoving said movable element; and an annular output member arrangedsubstantially coaxial with the fixed axis of said vibration member, forrotation about the fixed axis, in sliding frictional contact with saidannular rotor, and located between said annular rotor and said movingmechanism for actuating the moving mechanism in response to rotation ofsaid annular rotor, said annular output member being frictionallycontacted to each of said annular rotor and said moving mechanism suchthat a frictional engagement force between said vibration member andsaid annular rotor is greater than a frictional engagement force betweensaid output member and said annular rotor, and whereby rotation of saidannular rotor by vibration in said vibration member is absorbed bysliding contact between said output member and said rotor when anover-load is applied to said movable element.
 2. An apparatus accordingto claim 1, further comprising:a bar-shaped supporting member engagedwith said vibration member and integrally formed therewith along thefixed axis; and a holding member for holding said supporting member at apredetermined position.
 3. An apparatus according to claim 2, whereinsaid holding member engages said moving mechanism so as to receive athrust force of said moving mechanism.
 4. An apparatus according toclaim 2, wherein said movable element includes an optical lens.